US4162456A - Differential amplifying system - Google Patents

Differential amplifying system Download PDF

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Publication number
US4162456A
US4162456A US05/868,427 US86842778A US4162456A US 4162456 A US4162456 A US 4162456A US 86842778 A US86842778 A US 86842778A US 4162456 A US4162456 A US 4162456A
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US
United States
Prior art keywords
amplifier
terminal
differential
inverting input
output
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US05/868,427
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English (en)
Inventor
Henry J. Lukes
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Sundstrand Data Control Inc
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Sundstrand Data Control Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Sundstrand Data Control Inc filed Critical Sundstrand Data Control Inc
Priority to US05/868,427 priority Critical patent/US4162456A/en
Priority to DE19782853829 priority patent/DE2853829A1/de
Priority to SE7813445A priority patent/SE7813445A0/sv
Priority to GB79347A priority patent/GB2012138A/en
Priority to JP33679A priority patent/JPS5498554A/ja
Priority to IT47554/79A priority patent/IT1114508B/it
Priority to FR7900444A priority patent/FR2414266A1/fr
Application granted granted Critical
Publication of US4162456A publication Critical patent/US4162456A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/45—Differential amplifiers
    • H03F3/45071—Differential amplifiers with semiconductor devices only
    • H03F3/45479—Differential amplifiers with semiconductor devices only characterised by the way of common mode signal rejection

Definitions

  • This invention relates to differential amplifying systems and, more particularly, to a system for amplifying a differential component of a composite signal and rejecting the common mode component of the composite signal.
  • the gain of the differential amplifying systems known to the prior art is not adjustable without additional adjustment of the established impedance relationships.
  • the magnitude of the common mode component must be kept smaller than the supply voltage to the differential amplifiers to assure the complete rejection of the common mode component.
  • the circuit includes a main and an auxiliary amplifier.
  • the inputs of the main differential amplifier are coupled to a signal source which provides a signal having a differential component and a common mode component.
  • the differential component is amplified and the common mode component passes through the main differential amplifier without being amplified.
  • One input of the auxiliary differential amplifier is provided with the common mode component and the other input of the auxiliary differential amplifier is connected to ground.
  • the gain of the auxiliary differential amplifier is selected to attenuate the common mode component by an established value.
  • the outputs of the main and auxiliary amplifiers are applied to a voltage divider.
  • the voltage divider permits the unamplified common mode component from the main amplifier to be subtracted from the common mode component from the auxiliary amplifier.
  • the values of the impedances in the voltage divider are selected so that the common mode component is completely eliminated from the output signal.
  • FIGS. 1-3 are schematic diagrams of differential amplifying systems known to the prior art
  • FIG. 4 is a schematic diagram of a portion of the differential amplifying system according to the present invention.
  • FIG. 5 is a schematic diagram of the basic system according to the present invention.
  • FIG. 6 is a schematic diagram of the preferred embodiment of the system of FIG. 5, with additional circuit details shown;
  • FIG. 7 is a schematic diagram of a modified form of differential amplifying system embodying the invention wherein the inverting amplifier terminals are connected to a common signal source terminal.
  • a composite voltage source 10 includes a common-mode voltage source 12 and a differential voltage source 22, which is connected to inputs 14 and 16.
  • the gain of amplifier 18 depends upon whether a signal is applied to the noninverting input 14 or the inverting input 16. If it is desired to amplify the differential component Vd from source 22, and to eliminate the common mode component Vc from source 12, the following relationship must be established between resistors 24, 26, 28 and 30:
  • FIG. 2 another known differential amplifying system having three differential amplifiers is shown.
  • the noninverting inputs 32 and 34 of amplifiers 36 and 38, respectively, are coupled to composite voltage source 10.
  • the values of resistors 40 and 42 are selected to equal the value of resistors 44 and 46, respectively.
  • the outputs of amplifiers 36 and 38 are applied to inputs 14 and 16 of amplifier 18, as discussed in FIG. 1.
  • the lead resistance from the composite voltage source 10 does not affect the relationship of the resistances 24, 26, 28 and 30. Therefore, asymmetry of the resistance in the leads no longer affects the rejection of the common mode component.
  • FIG. 3 another differential amplifying system known to the prior art is shown.
  • Composite voltage source 10 is connected between the noninverting terminal 48 of amplifier 50 and the inverting terminal 52 of amplifier 54.
  • Amplifiers 50 and 54 are provided with the appropriate resistances to establish the desired gain.
  • the outputs of amplifiers 50 and 54 are coupled to a voltage divider consisting of resistors 56 and 58.
  • resistors 56 and 58 By selecting the relative values of resistors 56 and 58, the common mode component cancels, leaving the amplified differential component at the output.
  • any imbalance in resistance due to a difference in the lead length from composite voltage source 10 to amplifiers 50 and 54 can be accounted for by the appropriate selection of resistors 56 and 58 so that the circuit amplifies the differential component and rejects the common mode component.
  • the drawbacks discussed above with respect to FIG. 2 are still present in the circuit shown in FIG. 3.
  • Composite voltage source 10 is coupled to amplifier 60 so that the differential voltage source 22 is coupled between the inverting and the noninverting terminals thereof and the common mode component source 12 is coupled between one input terminal and ground 20.
  • Impedances 62 and 64 are selected to establish the gain of amplifier 60. Specifically, from well known formulae, which are valid for differential amplifiers having a high open loop gain, the output voltage of an amplifier being driven by its inverting input is
  • the gain of amplifier 60 is unity for the common mode component Vc from source 12, regardless of the characteristics of the impedances 62 and 64.
  • the unity transfer of the common mode component Vc is not affected by the values or character of impedances 64 and 62; so they can be resistive, reactive or complex, linear or nonlinear or each of them can be of another kind.
  • this circuit can process the differential component in many different ways; e.g., as a linear or nonlinear amplifier, or as an integrator or differentiator or as a waveform shaping circuit.
  • reference terminal 66 of power supply 68 for amplifier 60 it is preferable to connect reference terminal 66 of power supply 68 for amplifier 60 to the composite voltage source 10 rather than connecting reference terminal 66 to ground 20. If the power supply is so connected, amplifier 60 and its power supply 68 float with the common mode component from source 12 thereby permitting the amplifier 60 to operate with large common mode voltage without affecting its function with respect to the differential component. Thus, the amplifier is not responsive to variations in the common mode component, particularly if it is surrounded by electrostatic shield 70 connected to reference terminal 66.
  • the output of amplifier 60 includes the amplified differential component and the unamplified common mode component (see Equation 7), the latter component must be removed so that the output voltage includes only the differential component.
  • FIG. 5 The basic operation of the invention is illustrated in FIG. 5.
  • an auxiliary amplifier 72 and its associated resistors 74, 76 and 78 have been added to the circuit identical to that shown in FIG. 4 for removing the common mode component.
  • a voltage divider formed by impedances 80 and 82 is connected between the output of the main amplifier 60 and auxiliary amplifier 72.
  • the noninverting input of amplifier 72 is connected to ground 20.
  • the inverting input is coupled to the common mode component source 12 of composite voltage source 10 through resistors 74 and 76.
  • the ratio of the resistance 78 plus the right-hand portion of potentiometer 76 to the resistances 74 plus the left-hand portion of 76 establishes the gain of amplifier 72.
  • auxiliary amplifier 72 works in such a way that its output common mode component has an opposite polarity with respect to the output common mode component of the main amplifier 60.
  • Outputs of amplifiers 60 and 72 are connected to the ends of a voltage divider which consists of two impedances of the same character, e.g. of resistors 80 and 82.
  • the output terminal 84 is connected to a top on this voltage divider which is represented by the node between resistors 80 and 82.
  • the common mode component from amplifier 60 may be balanced out by the common mode component from amplifier 72. Specifically, if the ratio of resistor 82 to resistor 80 equals the absolute value of the gain of amplifier 72, as established by resistors 74, 76 and 78, the common mode component on output terminal 84 is zero.
  • the available output voltage swing of amplifier 72 is smaller than the magnitude of the common voltage from source 12, it is necessary that the absolute value of gain of amplifier 72 be less than unity so that the output voltage therefrom is not clipped. It may be desirable to further amplify the differential component by applying it to another amplifier stage, as will be discussed below.
  • FIG. 6 Illustrated in FIG. 6 is a circuit representing the preferred embodiment of the invention.
  • the differential amplifier system is driven by a capacitive transducer 86 which provides a composite signal as discussed above.
  • Capacitive transducer 86 is coupled to the input terminals of a so-called charge amplifier 60 through an interconnecting coax cable 88.
  • the shield 90 of coax cable 88 is secured to electrostatic shield 70.
  • Impedance 62 is represented by the internal capacitance of the transducer 86.
  • the value of impedance 64 is determined by the position of switch 92.
  • Impedance 64 consists of a set of selectable capacitors 96, 97 and 98. In addition, it contains a very high resistor 94 which establishes the position of the operating point.
  • the gain of amplifier 60 is adjustable over a broad range.
  • the voltage divider formed by resistors 80 and 82 may be of a selected ratio as, for example, 4:1, and is selected in accordance with the ratio of resistors 74, 76 and 78.
  • Resistor 76 may be in the form of a trim potentiometer for adjusting the gain of amplifier 72 within a very narrow range.
  • Output 84 may be connected to a two-position switch 100.
  • amplifier 102 When switch 100 is in a lower position, amplifier 102 provides a gain by an amount equal to
  • amplifier 102 provides an optional polarity inverter which in both positions delivers the same magnitude of output voltage.
  • the system disclosed herein has many applications in processing a differential component and eliminating a common mode component. Therefore, these applications are not limited to amplifying systems per se. Also, it is apparent that the teachings provided herein also apply to a noninverting configuration of the main differential amplifier, as well as the inverting configuration discussed above.
  • FIG. 7 A noninverting configuration is illustrated in FIG. 7 which differs from the circuit of FIG. 5 primarily in that the inverting input of the auxiliary inverting amplifier 72 is connected to the same terminal of the signal source 10 as the inverting input of the main amplifier 60.
  • Analysis of the circuit of FIG. 7 similar to that provided above for the circuits of FIGS. 5 and 6 will show that it is equally effective in rejecting the common mode portion of a signal.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Amplifiers (AREA)
US05/868,427 1978-01-10 1978-01-10 Differential amplifying system Expired - Lifetime US4162456A (en)

Priority Applications (7)

Application Number Priority Date Filing Date Title
US05/868,427 US4162456A (en) 1978-01-10 1978-01-10 Differential amplifying system
DE19782853829 DE2853829A1 (de) 1978-01-10 1978-12-13 Differenzverstaerkeranordnung
SE7813445A SE7813445A0 (sv) 1978-01-10 1978-12-29 Differential signalbehandlingsanordning med gemensam moddämpning
GB79347A GB2012138A (en) 1978-01-10 1979-01-05 Differential amplifying system
JP33679A JPS5498554A (en) 1978-01-10 1979-01-08 Differential amplifier
IT47554/79A IT1114508B (it) 1978-01-10 1979-01-08 Circuito amplificatore differenziale
FR7900444A FR2414266A1 (fr) 1978-01-10 1979-01-09 Dispositif de traitement differentiel de signaux

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US05/868,427 US4162456A (en) 1978-01-10 1978-01-10 Differential amplifying system

Publications (1)

Publication Number Publication Date
US4162456A true US4162456A (en) 1979-07-24

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Family Applications (1)

Application Number Title Priority Date Filing Date
US05/868,427 Expired - Lifetime US4162456A (en) 1978-01-10 1978-01-10 Differential amplifying system

Country Status (7)

Country Link
US (1) US4162456A (it)
JP (1) JPS5498554A (it)
DE (1) DE2853829A1 (it)
FR (1) FR2414266A1 (it)
GB (1) GB2012138A (it)
IT (1) IT1114508B (it)
SE (1) SE7813445A0 (it)

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4258329A (en) * 1978-03-22 1981-03-24 Pioneer Electronic Corporation Noise suppression system
US4346424A (en) * 1980-02-22 1982-08-24 Eaton Corporation Electronic remote control D.C. power controller and circuit breaker
US4352998A (en) * 1980-04-07 1982-10-05 Reliance Electric Company Common mode rejection coupler
US5121079A (en) * 1991-02-12 1992-06-09 Dargatz Marvin R Driven-common electronic amplifier
US5632280A (en) * 1995-03-03 1997-05-27 Heartstream, Inc. Method for circuit fault detection in differential signal detectors
US20040080365A1 (en) * 2002-07-25 2004-04-29 Honeywell International Inc. Method and apparatus for common-mode level shifting
US20050122170A1 (en) * 2003-12-04 2005-06-09 Kirby Patrick C. Op-amp configurable in a non-inverting mode with a closed loop gain greater than one with output voltage correction for a time varying voltage reference of the op-amp, and a method for correcting the output voltage of such an op-amp for a time varying voltage refer
CN113037229A (zh) * 2021-03-05 2021-06-25 广东尚永智控科技有限公司 适用于电磁水表的共模干扰抑制电路及二次仪表
CN114640349A (zh) * 2022-05-12 2022-06-17 苏州联讯仪器有限公司 一种差分信号采样电路、差分信号的采样方法及装置

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AT391559B (de) * 1984-08-10 1990-10-25 Schrack Elektronik Ag Schaltungsanordnung zur auswertung von von einer signalquelle gewonnenen wechselstromsignalen
US4720686A (en) * 1987-01-14 1988-01-19 Motorola, Inc. Circuit for converting a fully differential amplifier to a single-ended output amplifier
GB8809206D0 (en) * 1988-04-19 1988-05-25 Otec Electronics Ltd Amplifier circuit

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1334674A (en) * 1969-12-02 1973-10-24 Plessey Co Ltd Electrical circuit arrangements incorporating amplifiers
US4047122A (en) * 1976-02-11 1977-09-06 Westinghouse Electric Corporation Frequency compensated differential amplifier

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1334674A (en) * 1969-12-02 1973-10-24 Plessey Co Ltd Electrical circuit arrangements incorporating amplifiers
US4047122A (en) * 1976-02-11 1977-09-06 Westinghouse Electric Corporation Frequency compensated differential amplifier

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4258329A (en) * 1978-03-22 1981-03-24 Pioneer Electronic Corporation Noise suppression system
US4346424A (en) * 1980-02-22 1982-08-24 Eaton Corporation Electronic remote control D.C. power controller and circuit breaker
US4352998A (en) * 1980-04-07 1982-10-05 Reliance Electric Company Common mode rejection coupler
US5121079A (en) * 1991-02-12 1992-06-09 Dargatz Marvin R Driven-common electronic amplifier
US5632280A (en) * 1995-03-03 1997-05-27 Heartstream, Inc. Method for circuit fault detection in differential signal detectors
US5650750A (en) * 1995-03-03 1997-07-22 Heartstream, Inc. Common mode signal and circuit fault detection in differential signal detectors
US20040080365A1 (en) * 2002-07-25 2004-04-29 Honeywell International Inc. Method and apparatus for common-mode level shifting
US6924696B2 (en) * 2002-07-25 2005-08-02 Honeywell International Inc. Method and apparatus for common-mode level shifting
US20050122170A1 (en) * 2003-12-04 2005-06-09 Kirby Patrick C. Op-amp configurable in a non-inverting mode with a closed loop gain greater than one with output voltage correction for a time varying voltage reference of the op-amp, and a method for correcting the output voltage of such an op-amp for a time varying voltage refer
US6937099B2 (en) * 2003-12-04 2005-08-30 Analog Devices, Inc. Op-amp configurable in a non-inverting mode with a closed loop gain greater than one with output voltage correction for a time varying voltage reference of the op-amp, and a method for correcting the output voltage of such an op-amp for a time varying voltage reference
CN113037229A (zh) * 2021-03-05 2021-06-25 广东尚永智控科技有限公司 适用于电磁水表的共模干扰抑制电路及二次仪表
CN113037229B (zh) * 2021-03-05 2025-08-01 广东尚永智控科技有限公司 适用于电磁水表的共模干扰抑制电路及二次仪表
CN114640349A (zh) * 2022-05-12 2022-06-17 苏州联讯仪器有限公司 一种差分信号采样电路、差分信号的采样方法及装置

Also Published As

Publication number Publication date
IT7947554A0 (it) 1979-01-08
JPS5498554A (en) 1979-08-03
IT1114508B (it) 1986-01-27
SE7813445A0 (sv) 1979-07-11
GB2012138A (en) 1979-07-18
DE2853829A1 (de) 1979-07-12
FR2414266A1 (fr) 1979-08-03

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